RE: [Xen-ia64-devel] [PATCH] Add event callback for xen/ia64

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Alex Williamson [mailto:alex.williamson@xxxxxx]
>Sent: 2006年4月12日 13:24
>>    It appears dom0 is not affected and has good throughput.  Here's
>an
>> interesting observation though; if I wget from dom0 and domU at the
>same
>> time, dom0 is a little slower (~82MB/s), but the domU throughput
>> actually increases while the wget in dom0 is running.  According to
>> nload, domU's throughput nearly doubles for the brief time dom0's
>wget
>> is running.  Even wget'ing a different file off the server with dom0
>> causes domUs wget to speed up.  Perhaps an indication that your
>priority
>> hunch is correct?  Thanks,
>
>   In contrast, w/o the event channel patch, domU is unaffected by a
>concurrent wget in dom0 (fairly constant ~10.5MB/s).  However, dom0
>only
>runs at around 9MB/s while domU's transfer is running.
>
>       Alex
>

This may be explained as following:

Before apply my patch, all the inter-domain events are bound a
vector 233 which is higher than any external device interrupts. 
In this case, vnif request is always handled immediately without 
delay however real nic interrupt is responded with lower priority. 
By this way, the vnif path is high satisfied, however the normal
eth0 driver of dom0 is affected a lot by virtual driver(vbd/vnif). 
Thus dom0's network output is decreased in this way

After applying my patch, all the inter-domain events are placed 
lower than all interrupt vectors. So in contrast, the real nic traffic 
can be handled immediately while requests from virtual drivers 
are delayed/pended a lot by any interrtups. So domU network 
output decreased.

Actually this is why event channel mechanism is proposed by 
xen/x86 and we're now approaching ia64 to this direction too. 
Current patch I sent out is only an intermediate step which have 
two separate paths for events and interrupts. Finally there'll be 
only one event path and at that time we can do more fine-grained 
control to the priority per event.

So do you think whether this patch is available for check-in now? 
We can do more accurate tuning after the whole model is ready 
and p2m patch is merged in.

Anyway, I'm still making some measurement now. I may provide 
a version matching current behavior if you like, for example 
increasing event path priority, which however may not worth doing
since it's only temporary solution. :-)

Thanks,
Kevin

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